This invention relates to injecting seawater into a subterranean oil reservoir to displace oil toward a production location. More particularly, the invention relates to a waterflood oil recovery process in which the flood water is, preferably, ammoniated and nitrited seawater.
As indicated in "How to Treat Seawater for Injection Projects" by D. L. Carlberg in World Oil, July 1979, page 67, "With careful treatment the virtually unlimited supply of readily available ocean water can be used successfully as a source of injection fluid for offshore or near shore pressure maintenance of water flood projects." The article mentions that organic growths in seawater range from bacteria to sea weed, barnacles and fish, and indicates that a basic treatment scheme, for seawater to be used as an injection medium, includes adding a biocide, filtering and deoxygenating and possibly, scale inhibiting the seawater.
An article by R. W. Mitchell in Journal of Petroleum Technology, June 1978, page 887, is titled "The Forties Field Seawater Injection System". The article recommends similar basic treatments of the seawater. It also describes a particular advantage of using chlorine or a hypochlorite as a biocide in combination with deoxygenation by stripping with production gas and addition of ammonium bisulfite, where the final pH of the water is about 7.5 to 9. The article mentions that although few scavengers can reduce the oxygen to less than 50 ppm, this can be achieved by bisulfite, but only if chlorine is present in the system.
An article by C. C. McCune in Journal of Petroleum Technology, October 1982, at page 2265, is titled "Seawater Injection Experience: An Overview". It mentions that seawater is being used more and more as the water injected into subterranean reservoirs and recommends substantially the same basic treatments of the seawater. It also indicates that adding chlorine as a biocide and SO.sub.2 as an oxygen scavenger tends to reduce the pH of the seawater from a normal of about 8 to about 5.8.